It is becoming increasingly difficult to ignore the complexity of software products. Software metrics are proposed to help show indications for quality, size, complexity, etc. of software products. In this book, software metrics related to complexity are developed and evaluated. A dataset of many open source projects is built to assess the value of the developed metrics. Comparisons and correlations are conducted among the different tested projects. A classification is proposed to classify software code into different levels of complexity. The results showed that measuring the complexity of software products based on decision coverage gives a significant indicator of degree of complexity of those software products.